This version of "Constant", by Mister Vapor, uses blurred and effected sferics, which are sounds emitted by the earth. Less stable than the earliest of Constants, "Constant 25" nonetheless provides a nice, consistent floating sound bed perfect for deep listening.
"Constant" pieces, for those unfamiliar, are musical works based on being as minimal as possible-- finding the least possible thing necessary for listening. These pieces tend to be drone in nature. The original Constant appeared on Webbed Hand Records ( www.webbedhandrecords.com ), and others have been released at the TZP Drone Company ( http://www.archive.org/details/tzpdc ) and also here at Treetrunk.
More info. on Mister Vapor: www.mystifiedmusic.com